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Deliverability Letter

Feedback Loop (FBL)

Also known as: FBL, Complaint Feedback Loop

A feedback loop is a system where inbox providers tell you when someone marks your emails as spam. It gives you a clear signal so you can remove complainers fast and protect your sender reputation.

Feedback loops are alerts from inbox providers that tell you when someone marks your email as spam. Instead of guessing who is unhappy, you get a clear signal tied to a real subscriber. This helps you see which emails cause complaints. It is one of the basic tools for keeping your email list healthy.

These alerts protect your sender reputation. When you know who complained, you can stop emailing them before more damage happens. Over time you will notice patterns in which subject lines, offers, or lists lead to more spam clicks. That detail lets you fix problems early so more of your email lands in the inbox.

For most senders the hard work happens behind the scenes in tools like Bento, which receive and process this data for you. Your job is to review complaint numbers, remove complainers, and adjust how often and what you send. Aim to keep complaints very low, around 0.1 percent or less of delivered emails. If you see a spike, pause and clean your list before sending again.